The present invention relates to a hybrid scan type ion implantation apparatus in which an ion beam is electrostatically scanned and a target is mechanically scanned in the direction perpendicular to the ion beam.
FIG. 1 shows a prior art ion implantation apparatus.
In this ion implantation apparatus, after an ion beam 2 is extracted from an ion source, which is subjected to mass analysis, acceleration, trimming, and so forth, if necessary, the ion beam 2 is electrostatically scanned in the X direction (for example, in the horizontal direction) by a pair of scanning electrodes 4 to which a scanning voltage is applied from a scanning power supply 12 so as to plainly spread the ion beam 2 in the X direction.
The scanning power supply 12 is provided with a generator 121 for generating a triangle wave signal at a particular frequency and high voltage amplifiers 122 and 123 for raising the voltage of the signal and for outputting reverse polarity voltages VX and -VX, respectively.
On the other hand, a target 6 (for example, a wafer) is held by a holder 8 in the radiation area of the ion beam 2. The target 6 is mechanically scanned by a drive unit 10 in the Y direction perpendicular to the X direction (for example, in the vertical direction). This mechanical scanning operation is associated with the scanning operation of the ion beam 2 so as to equally implant ions into the entire surface of the target 6.
In the ion implantation apparatus described above, the route of the ion beam 2 is varied in the following conditions.
(1) The properties of the ion beam 2 itself (for example, its energy, divergence angle, emittance, density, ion type, and so forth), PA1 (2) The mechanical properties of the scanning electrodes 4 (for example, its parallelism, helix angle, position against the ion beam 2, and so forth), PA1 (3) The electrical properties of the scanning electrodes 4 (for example, scanning voltage applied thereto, frequency, and so forth), and PA1 (4) The conditions in the vicinity of the route of the ion beam 2.
The conditions (2) and (4) of the above conditions are intrinsic to the ion implantation apparatus and thereby they do not vary depending on the implantation conditions. However, the conditions (1) and (3) vary depending on the implantation conditions. Moreover, the route of the ion beam 2 varies by a combination of each condition rather than by a single condition.
When the variation of the route occurs equally in the entire range of the beam route scanned on the surface of the target 6, no problem arises. However, when a part of the route varies, the scanning speed of the ion beam 2 varies only at a particular portion, thereby badly affecting the uniformity of the ion implantation to the target 6.
Normally, the nonuniformity of ion implantation can be maintained to 1% or less. However, recently, semiconductor devices are being formed on the surface of the target 6 with high integration and high performance. Thus, much higher uniformity is required than before.